<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
  <canvas id="canvas" style="width: 300px;height: 300px;"></canvas>
  <script>
    const el = document.getElementById('canvas')
    const app = el.getContext('2d')
    //
    app.fillStyle = 'red'
    app.fillRect(0, 0 , 300, 300)


  </script>
</body>
</html>
